My rubella test came back positive, I was told that this is a good thing while I am pregnant because this means that I don't have it and I don't have to worry about passing it to my baby. Is this true?

Yes, this is correct. If the rubella (german measles) test is 'positive', this means that you have been successfully vaccinated in the past and have antibodies to the virus that are circulating in your bloodstream. If you come into contact with the virus, your antibodies mean (in the vast majority of cases) that you are immune and should not contract the infection. A 'negative' test means you don't have these antibodies and are therefore potentially susceptible to catching rubella.